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Avalanche Forecast

Archived

Dec 29th, 2013–Dec 30th, 2013

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Confidence

Poor - Due to the number of field observations

Weather Forecast

Tonight and Monday: Periods of snow 20-30 cm. The freezing level is near 1500 m lowering to 1000 m in the evening. Winds are strong from the SW. Tuesday: A mix of sun and cloud with a chance of flurries. The freezing level is near 800-1000 m and winds are moderate to strong from the west. Wednesday: Another frontal system should arrive bringing periods of snow. The freezing level is around 500-800 m.

Avalanche Summary

There are no new reports from the region. Another pulse of precipitation and strong ridge top winds overnight Saturday may have tipped off a natural avalanche cycle in some areas. Touchy wind slabs probably built in N-E facing terrain well into treeline. Loose wet avalanches were possible below treeline as temperatures warmed near the tail end of the system.

Snowpack Summary

Southern Sections: The latest weather system dropped another 20-30 cm of snow (with more on the way), bringing the total snowfall over the past week to around 150 cm. The recent storm snow is likely "upside down" feeling, with heavier snow on top due to warming at the tail end of the system. Winds were also very strong from the SW most likely creating fresh wind slabs in exposed lee terrain at all elevations. Freezing levels climbed to near 1500 m resulting in moist snow or rain below treeline. Much of the low elevation snowpack has been washed away by recent rain.Northern Sections: Another 15 cm of snow fell on Saturday night bringing the total snowfall over the past week to around 80 cm. Weaknesses may still exist within the recent storm snow. Fresh dense wind slabs are likely in exposed lee terrain and cross-loaded features at all elevations. A recently buried surface hoar layer is now down around 80 cm and is likely primed for rider triggering. A facet/crust layer exists near the base of the snowpack, primarily on higher NW through E facing slopes. Triggering this layer may be unlikely, but if triggered the resulting avalanche would be very large and dangerous.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.